Blue phase liquid crystal system, method of operation and its use

Abstract

An optical system contains a liquid crystal cell (1), to the liquid crystal layer (11) of which an E-field can be applied transversely to the plane of the layer. A light source (3) sends to the liquid crystal cell (1) a beam of rays parallel to the field direction. The liquid crystal is in the form of a chiral, optically isotropic phase ("blue phase"). This phase has a field-dependent optical density for the incident light and is matched to the light wavelength such that no selective reflection takes place. Such a cell is also optically isotropic in the presence of an E-field, switches rapidly and requires no interface orientation. Its preferred fields of use are: intensity modulation of light of a given wavelength, or as a phase grid in a schlieren-optical system, an etalon in a laser, or a light switch.

What is claimed is: 
     
       1. An optical system for modifying light transmitted therethrough comprising: (1) a liquid crystal cell comprising (a) two polarizer-free carrier plates facing one another, each having on its surface facing the other, a patterned electrode, and (b) a liquid crystal layer enclosed between the carrier plates;   (2) an AC voltage source operationally connected to the electrodes and which in operation produces in the liquid crystal layer an electrical field which is directed essentially perpendicularly to the plane of the layer;   (3) a light source placed in front of the liquid crystal cell which in operation impinges a beam of light onto the liquid crystal cell in a direction which essentially corresponds to the direction of the electric field, said light consisting essentially of a frequency or frequencies to which the liquid crystal layer is essentially transparent and has a field-dependent optical density; and   (4) an optical element utilizing the light transmitted through the liquid crystal layer,   wherein the liquid crystal layer is in a blue phase during operation of the system and does not selectively filter out wavelength components of the light passing through.   
     
     
       2. A system of claim 1, wherein the local dielectric anisotropy of the liquid crystal layer has a positive value greater than 3 in the field-free state. 
     
     
       3. A system of claim 1, wherein the local dielectric anisotropy of the liquid crystal layer has a positive value greater than 7 in the field-free state. 
     
     
       4. A system of claim 1, wherein the local dielectric anisotropy of the liquid crystal layer has a negative value less than -1 in the field-free state. 
     
     
       5. A system of claim 1 wherein the local dielectric anisotropy of the liquid crystal layer has different signs above and below a certain alternating voltage frequency. 
     
     
       6. A system of claim 1 wherein the liquid crystal layer is a mixture of at least one nematic component and one chiral component. 
     
     
       7. A system of claim 1 wherein the liquid crystal layer has a thickness of 20 μm to 250 μm. 
     
     
       8. A system of claim 1 wherein the liquid crystal layer has a thickness of 25 μm to 100 μm. 
     
     
       9. A system of claim 1 wherein the frequency of the alternating voltage is 30 Hz to 10 5  Hz. 
     
     
       10. A system of claim 1 wherein the frequency of the alternating voltage is 500 Hz to 10 4  Hz. 
     
     
       11. A system of claim 9 wherein the alternating voltage is a square wave voltage. 
     
     
       12. In an optical system for intensity modulation of light of a certain wavelength comprising a liquid crystal cell, a voltage source and a light source, the improvement wherein the optical system is that of claim 1. 
     
     
       13. In a schlieren-optical system, comprising a liquid crystal cell, a voltage source and a light source, the improvement wherein the optical system is that of claim 12. 
     
     
       14. In a display system for showing motion pictures, the improvement wherein the display system comprises a schlieren-optical system of claim 13. 
     
     
       15. In an optical system effective as a lens comprising a liquid crystal cell, a voltage source and a light source, the improvement wherein the optical system is that of claim 12. 
     
     
       16. An optical system of claim 15 wherein the light source is a laser. 
     
     
       17. In an optical system effective as a lens of variable focal length, comprising a liquid crystal cell, a voltage source and a light source, the improvement wherein the optical system is that of claim 12. 
     
     
       18. In an optical system effective as a light switch, comprising a liquid crystal cell, a voltage source and a light source, the improvement wherein the optical system is that of claim 12. 
     
     
       19. An optical system of claim 1 wherein the liquid crystal phase is a blue phase. 
     
     
       20. A method of influencing light comprising directing the light onto the liquid crystal cell of claim 1.